This invention is concerned with powder dosing apparatus especially, but not exclusively, for use in the priming of explosive devices, for example centrefire or rimfire cartridges.
In our published UK patent specification No. 1569874 we describe and claim a method of priming a plurality of explosive devices which, in its preferred form, includes the steps of dosing a quantity of a substantially dry powdery "premix" into an element, eg. a centrefire capshell or rimfire case, of each device, followed by dosing a quantity of a liquid reaction medium, typically water, into the elements so as to form, in situ, a quantity of moist primer in each element. The moist primer is subsequently dried. More particularly, the premix is a relatively insensitive mixture (relative, that is, to the resulting primer) comprising at least two compounds that will, in the presence of a liquid reaction medium, react together forming a primary explosive compound and further comprising other conventional ingredients of a primer, the compounds and ingredients being present in predetermined proportions. Thus, upon addition of the liquid reaction medium, the two (or more,if appropriate) compounds react together forming the primary explosive compound in admixture with the further ingredients present in the premix. By way of example, a typical premix for use in priming rimfire cartridges comprises, in predetermined proportions, lead monoxide, styphnic acid, a sensitiser such as tetrazene, an oxidiser such as barium nitrate and a frictionator such as glass. A typical primix for use in priming centrefire cartridges, for example shotgun cartridges, in which the primary is contained in a capshell, may comprise lead monoxide, styphnic acid, a sensitizer such as tetrazene, oxidisers such as barium nitrate and lead dioxide, and fuels such as calcium silicide and antimony sulphide. In both cases, the lead monoxide and styphnic acid react together, in the presence of water as the reaction medium, to yield the primary explosive compound, lead styphate, whilst the other ingredients retain their identity in the final primer.
The method described above is relatively safe compared to conventional priming methods since it avoids the need to store and handle the primary explosive compound, such as lead styphate, and mixtures containing it, in bulk. Because of this, the method is suited to full automation. Hitherto, we have dosed the powdery premix, from bulk quantities thereof, simultaneously into a large number of capshells or cases using conventional priming plate techniques. Whilst this has proved satisfactory, it is difficult to guarantee that the correct quantity of premix will be dosed into each and every capshell or case as is necessary if eventual "misfires" are to be avoided.